title: Photochemistry of aqueous pyruvic acid.
abstract: The study of organic chemistry in atmospheric aerosols and cloud formation is of interest in predictions of air quality and climate change. It is now known that aqueous phase chemistry is important in the formation of secondary organic aerosols. Here, the photoreactivity of pyruvic acid (PA; CH3COCOOH) is investigated in aqueous environments characteristic of atmospheric aerosols. PA is currently used as a proxy for α-dicarbonyls in atmospheric models and is abundant in both the gas phase and the aqueous phase (atmospheric aerosols, fog, and clouds) in the atmosphere. The photoreactivity of PA in these phases, however, is very different, thus prompting the need for a mechanistic understanding of its reactivity in different environments. Although the decarboxylation of aqueous phase PA through UV excitation has been studied for many years, its mechanism and products remain controversial. In this work, photolysis of aqueous PA is shown to produce acetoin (CH3CHOHCOCH3), lactic acid (CH3CHOHCOOH), acetic acid (CH3COOH), and oligomers, illustrating the progression from a three-carbon molecule to four-carbon and even six-carbon molecules through direct photolysis. These products are detected using vibrational and electronic spectroscopy, NMR, and MS, and a reaction mechanism is presented accounting for all products detected. The relevance of sunlight-initiated PA chemistry in aqueous environments is then discussed in the context of processes occurring on atmospheric aerosols.
authors.affiliation: Department of Chemistry and Biochemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309, USA.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Griffith
authors.forename: Barry K
authors.initials: BK
authors.lastname: Carpenter
authors.forename: Richard K
authors.initials: RK
authors.lastname: Shoemaker
authors.forename: Veronica
authors.initials: V
authors.lastname: Vaida
mesh_terms: D019342:Acetic Acid / Q000737:chemistry; D000093:Acetoin / Q000737:chemistry; D000336:Aerosols / Q000737:chemistry*; D001272:Atmosphere / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D010777:Photochemistry / Q000379:methods*; D010782:Photolysis; D019289:Pyruvic Acid / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000336:Aerosols; D014867:Water; D019344:Lactic Acid; D019289:Pyruvic Acid; D000093:Acetoin; D019342:Acetic Acid
keywords: atmospheric chemistry; sunlight-initiated chemistry